Radio communications systems require the use of amplifiers to boost signals to power levels suitable for transmission. Such increased levels are provided by transmitter power amplifiers. Power amplifiers require significant power to amplify signals for transmission and management of available power resources is essential for performance reasons. In communication transceivers having substantially unlimited available power. Power management is used primarily to reduce installation size and reduce heat generation. Power management is of more concern in portable transceivers where conservation of power and efficient use of that power translates directly into increased performance and customer satisfaction.
Because power amplifiers typically utilize a substantial amount of power, conservation and efficiency of power resources falls upon using high efficiency amplifier configurations and stages within the communication transceiver. Therefore amplifier components such as the intermediary amplifiers and modulators must conserve as much power as possible to improve overall portable transceiver usability between battery charges.
In addition to power conservation techniques, different types of amplifiers and modulators have differing levels of efficiency. Furthermore, amplifiers typically operate at power levels that are less than their maximum power and efficiency levels. Operation at these "backoff" levels further reduces the overall efficiency of the devices.
For example, operation in more than -6 dB backoff is commonly encountered in most applications. Most amplifiers exhibit low efficiency of operation in this region, e.g., &lt;30%. Linear amplifiers typically operate at only about 20% efficiency or less when they are operated at -10 dB below their maximum power level.
When a device is operated in a linear mode, it dissipates considerably more power than when it is operated in a switching mode. Class-S modulators operate in the switching mode and therefore dissipate much less power and are therefore more conducive to portable communication applications.
Accordingly, there is a significant need for a method and apparatus for amplifying with a higher-efficiency an input signal having an envelope over a wide dynamic power range.